Disposable absorbent product having biodisintegratable nonwovens with improved fluid management properties

ABSTRACT

Disclosed is a biodisintegratable nonwoven material having improved fluid management properties. The biodisintegratable nonwoven material demonstrates a higher contact angle hysteresis, quicker intake times, and improved skin dryness as compared to prior art nonwoven materials. In addition, these biodisintegratable nonwoven materials also exhibit high wetting rates, which is unexpected based upon the higher hysteresis values. The nonwoven material may be produced using thermoplastic compositions which comprise an unreacted mixture of an aliphatic polyester polymer as a continuous phase, polyolefin microfibers as a discontinuous phase encased within the aliphatic polyester polymer continuous phase, and a compatibilizer for the aliphatic polyester polymer and the polyolefin microfibers. The multicomponent fiber exhibits substantial biodisintegratable properties and good wettability yet is easily processed. The biodisintegratable nonwoven materials may be used in a disposable absorbent product intended for the absorption of fluids such as body fluids.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part patent application of U.S.patent application Ser. No. 09/327,864, filed on Jun. 8, 1999, now U.S.Pat. No. 6,197,237 which is a divisional patent application of U.S.patent application Ser. No. 08/995,982, filed on Dec. 22, 1997, now U.S.Pat. No. 5,952,088.

FIELD OF THE INVENTION

The present invention relates to a disposable absorbent product having abiodisintegratable nonwoven material having improved fluid managementproperties. The nonwoven material may be produced from polymer blends.These blends may include multicomponent fibers. These multicomponentfibers comprise an unreacted mixture of an aliphatic polyester polymeras a continuous phase, polyolefin microfibers as a discontinuous phaseencased within the aliphatic polyester polymer continuous phase, and acompatibilizer for the aliphatic polyester polymer and the polyolefinmicrofibers. The multicomponent fiber exhibits substantialbiodisintegratable properties yet is easily processed. Thebiodisintegratable nonwoven materials may be used in a disposableabsorbent product intended for the absorption of fluids such as bodyfluids.

BACKGROUND OF THE INVENTION

Disposable absorbent products currently find widespread use in manyapplications. For example, in the infant and child care areas, diapersand training pants have generally replaced reusable cloth absorbentarticles. Other typical disposable absorbent products include femininecare products such as sanitary napkins or tampons, adult incontinenceproducts, and health care products such as surgical drapes or wounddressings. A typical disposable absorbent product generally comprises acomposite structure including a liquid-permeable topsheet, a fluidacquisition layer, an absorbent structure, and a liquid-impermeablebacksheet. These products usually include some type of fastening systemfor fitting the product onto the wearer.

Disposable absorbent products are typically subjected to one or moreliquid insults, such as of water, urine, menses, or blood, during use.As such, the outer cover materials of the disposable absorbent productsare typically made of liquid-insoluble and liquid impermeable materials,such as polypropylene films, that exhibit a sufficient strength andhandling capability so that the disposable absorbent product retains itsintegrity during use by a wearer and does not allow leakage of theliquid insulting the product.

Although current disposable baby diapers and other disposable absorbentproducts have been generally accepted by the public, these productsstill have need of improvement in specific areas. For example, manydisposable absorbent products can be difficult to dispose of. Forexample, attempts to flush many disposable absorbent products down atoilet into a sewage system typically lead to blockage of the toilet orpipes connecting the toilet to the sewage system. In particular, theouter cover materials typically used in the disposable absorbentproducts generally do not disintegrate or disperse when flushed down atoilet so that the disposable absorbent product cannot be disposed of inthis way. If the outer cover materials are made very thin in order toreduce the overall bulk of the disposable absorbent product so as toreduce the likelihood of blockage of a toilet or a sewage pipe, then theouter cover material typically will not exhibit sufficient strength toprevent tearing or ripping as the outer cover material is subjected tothe stresses of normal use by a wearer.

Furthermore, solid waste disposal is becoming an ever increasing concernthroughout the world. As landfills continue to fill up, there has beenan increased demand for material source reduction in disposableproducts, the incorporation of more recyclable and/or degradablecomponents in disposable products, and the design of products that canbe disposed of by means other than by incorporation into solid wastedisposal facilities such as landfills.

As such, there is a need for new materials that may be used indisposable absorbent products that generally retain their integrity andstrength during use, but after such use, the materials may be moreefficiently disposed of. For example, the disposable absorbent productmay be easily and efficiently disposed of by composting. Alternatively,the disposable absorbent product may be easily and efficiently disposedof to a liquid sewage system wherein the disposable absorbent product iscapable of being degraded.

Although degradable monocomponent fibers are known, problems have beenencountered with their use. In particular, known degradable fiberstypically do not have good thermal dimensional stability such that thefibers usually undergo severe heat-shrinkage due to the polymer chainrelaxation during downstream heat treatment processes such as thermalbonding or lamination.

In contrast, polyolefin materials, such as polypropylene, typicallyexhibit good thermal dimensional stability but also have problemsassociated with their use. In particular, polyolefin fibers typicallyare hydrophobic and, and such, exhibit poor wettability, thus limitingtheir use in disposable absorbent products intended for the absorptionof fluids such as body fluids. Although surfactants can be used toimprove the wettability of polyolefin fibers, the use of suchsurfactants introduces additional problems such as added cost,fugitivity or permanence, and toxicity. Furthermore, polyolefin fibersare generally not biodisintegratable or compostable.

It would therefore be desirable to prepare a biodisintegratable nonwovenmaterial which includes fibers that exhibit the thermal dimensionalstability of polyolefin materials yet are substantiallybiodisintegratable and are also wettable without the use of surfactants.A simple solution to this desire would be to simply mix a polyolefinmaterial with a degradable material so as to gain the benefits of usingboth materials. However, the components of a multicomponent fibergenerally need to be chemically compatible, so that the componentseffectively adhere to each other, and have similar rheologicalcharacteristics, so that the multicomponent fiber exhibits minimumstrength and other mechanical and processing properties. It hastherefore proven to be a challenge to those skilled in the art tocombine components that meet these basic processing needs as well asmeeting the desire that the entire multicomponent fiber be effectivelysubstantially degradable and hydrophilic.

It is therefore desirable to provide a biodisintegratable nonwovenmaterial which includes multicomponent fibers which are substantiallydegradable in the environment. It is also desirable to provide asubstantially degradable multicomponent fiber which has good thermaldimensional stability and is hydrophilic without the substantial use ofsurfactants. Finally, it is also desirable to provide abiodisintegratable nonwoven material having a substantially degradablemulticomponent fiber which is easily and efficiently prepared and whichis suitable for use in preparing these biodisintegratable nonwovenmaterials.

SUMMARY OF THE INVENTION

The present invention concerns a biodisintegratable nonwoven materialthat is substantially biodisintegratable and yet which is easilyprepared and readily processable into desired final structures.

One aspect of the present invention concerns a biodisintegratablenonwoven material which includes a thermoplastic composition thatcomprises a mixture of a first component, a second component, and athird component.

One embodiment of such a thermoplastic composition comprises anunreacted mixture of an aliphatic polyester polymer as a substantiallycontinuous phase, polyolefin microfibers as a substantiallydiscontinuous phase encased within the aliphatic polyester polymersubstantially continuous phase, and a compatibilizer for the aliphaticpolyester polymer and the polyolefin microfibers.

In another aspect, the present invention concerns a biodisintegratablenonwoven material which includes a multicomponent fiber that issubstantially degradable and yet which is easily prepared and readilyprocessable into desired final structures.

One aspect of the present invention concerns a biodisintegratablenonwoven material which includes a multicomponent fiber that comprisesan unreacted mixture of an aliphatic polyester polymer as asubstantially continuous phase, polyolefin microfibers as asubstantially discontinuous phase encased within the aliphatic polyesterpolymer substantially continuous phase, and a compatibilizer for thealiphatic polyester polymer and the polyolefin microfibers.

One embodiment of such a nonwoven structure is a fluid acquisition layeruseful in a disposable absorbent product.

One aspect of the present invention concerns a multicomponent fiber thatincludes an unreacted thermoplastic mixture of an aliphatic polyesterpolymer as a substantially continuous phase, polyolefin microfibers as asubstantially discontinuous phase encased within the aliphatic polyesterpolymer substantially continuous phase, and a compatibilizer for thealiphatic polyester polymer and the polyolefin microfibers as onecomponent of the multicomponent fiber. The fiber may be in anyconfiguration such that the thermoplastic mixture is exposed to thefiber surface as in sheath-core, eccentric sheath-core, side-by-side, orany other configuration. Such fibers could be made in to any type ofnonwoven material.

In another aspect, the present invention concerns a disposable absorbentproduct comprising the biodisintegratable nonwoven material disclosedherein.

In another aspect, the present invention concerns a process forpreparing the biodisintegratable nonwoven material disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a disposable absorbent producthaving a biodisintegratable nonwoven material which demonstrates highercontact angle hysteresis, quicker intake times, and improved skindryness as compared to prior art nonwoven materials. In addition, thesebiodisintegratable nonwoven materials also exhibit high wetting rates,which is unexpected based upon the higher hysteresis values.

These biodisintegratable nonwoven materials preferably include athermoplastic composition which includes a first component, a secondcomponent, and a third component. As used herein, the term“thermoplastic” is meant to refer to a material that softens whenexposed to heat and substantially returns to its original condition whencooled to room temperature.

It has been discovered that, by using an unreacted mixture of analiphatic polyester polymer as a substantially continuous phase,polyolefin microfibers as a substantially discontinuous phase encasedwithin the aliphatic polyester polymer substantially continuous phase,and a compatibilizer for the aliphatic polyester polymer and thepolyolefin microfibers, a thermoplastic composition may be preparedwherein such thermoplastic composition is substantially degradable yetwhich thermoplastic composition is easily processable into nonwovenstructures that exhibit effective fibrous mechanical properties andliquid handling properties.

The first component in the thermoplastic composition is an aliphaticpolyester polymer. Suitable aliphatic polyester polymers include, butare not limited to, poly(lactic acid), polybutylene succinate,polybutylene succinate-co-adipate, polyhydroxybutyrate-co-valerate,polycaprolactone, sulfonated polyethylene terephthalate, mixtures ofsuch polymers, or copolymers of such polymers.

In one embodiment of the present invention, it is desired that thealiphatic polyester polymer used is poly(lactic acid). Poly(lactic acid)polymer is generally prepared by the polymerization of lactic acid.However, it will be recognized by one skilled in the art that achemically equivalent material may also be prepared by thepolymerization of lactide. As such, as used herein, the term“poly(lactic acid) polymer” is intended to represent the polymer that isprepared by either the polymerization of lactic acid or lactide.

Lactic acid and lactide are known to be asymmetrical molecules, havingtwo optical isomers referred to, respectively, as the levorotatory(hereinafter referred to as “L”) enantiomer and the dextrorotatory(hereinafter referred to as “D”) enantiomer. As a result, bypolymerizing a particular enantiomer or by using a mixture of the twoenantiomers, it is possible to prepare different polymers that arechemically similar yet which have different properties. In particular,it has been found that by modifying the stereochemistry of a poly(lacticacid) polymer, it is possible to control, for example, the meltingtemperature, melt rheology, and crystallinity of the polymer. By beingable to control such properties, it is possible to prepare amulticomponent fiber exhibiting desired melt strength, mechanicalproperties, softness, and processability properties so as to be able tomake attenuated, heat set, and crimped fibers.

It is generally desired that the aliphatic polyester polymer be presentin the thermoplastic composition in an amount effective to result in thethermoplastic composition exhibiting desired properties. The aliphaticpolyester polymer will be present in the thermoplastic composition in aweight amount that is less than 100 weight percent, beneficially betweenabout 45 weight percent to about 90 weight percent, suitably betweenabout 50 weight percent to about 88 weight percent, and more suitablybetween about 55 weight percent to about 70 weight percent, wherein allweight percents are based on the total weight amount of the aliphaticpolyester polymer, the polyolefin microfiber, and the compatibilizerpresent in the thermoplastic composition. The compositional ratio of thethree components in the thermoplastic composition is generally importantto maintaining the substantial biodegradability of the thermoplasticcomposition because the aliphatic polyester polymer generally needs tobe in a substantially continuous phase in order to maintain access tothe biodisintegratable portion of the thermoplastic composition. Anapproximation of the limits of component ratios can be determined basedon the densities of the components. The density of a component isconverted to a volume (assume 100 g of each component), the volumes ofthe components are added together for a total thermoplastic compositionvolume and the components weight averages calculated to establish theapproximate minimum ratio of each component needed to produce athermoplastic composition with a volumetric majority of the aliphaticpolyester polymer in the blend.

It is generally desired that the aliphatic polyester polymer exhibit aweight average molecular weight that is effective for the thermoplasticcomposition to exhibit desirable melt strength, fiber mechanicalstrength, and fiber spinning properties. In general, if the weightaverage molecular weight of an aliphatic polyester polymer is too high,this represents that the polymer chains are heavily entangled which mayresult in a thermoplastic composition comprising that aliphaticpolyester polymer being difficult to process. Conversely, if the weightaverage molecular weight of an aliphatic polyester polymer is too low,this represents that the polymer chains are not entangled enough whichmay result in a thermoplastic composition comprising that aliphaticpolyester polymer exhibiting a relatively weak melt strength, makinghigh speed processing very difficult. Thus, aliphatic polyester polymerssuitable for use in the present invention exhibit weight averagemolecular weights that are beneficially between about 10,000 to about2,000,000, more beneficially between about 50,000 to about 400,000, andsuitably between about 100,000 to about 300,000. The weight averagemolecular weight for polymers or polymer blends can be determined usinga method as described in the Test Methods section herein.

It is also desired that the aliphatic polyester polymer exhibit apolydispersity index value that is effective for the thermoplasticcomposition to exhibit desirable melt strength, fiber mechanicalstrength, and fiber spinning properties. As used herein, “polydispersityindex” is meant to represent the value obtained by dividing the weightaverage molecular weight of a polymer by the number average molecularweight of the polymer. In general, if the polydispersity index value ofan aliphatic polyester polymer is too high, a thermoplastic compositioncomprising that aliphatic polyester polymer may be difficult to processdue to inconsistent processing properties caused by polymer segmentscomprising low molecular weight polymers that have lower melt strengthproperties during spinning. Thus, it is desired that the aliphaticpolyester polymer exhibits a polydispersity index value that isbeneficially between about 1 to about 15, more beneficially betweenabout 1 to about 4, and suitably between about 1 to about 3. The numberaverage molecular weight for polymers or polymer blends can bedetermined using a method as described in the Test Methods sectionherein.

In the present invention, it is desired that the aliphatic polyesterpolymer be biodegradable. As a result, the nonwoven material includingthe aliphatic polyester polymer will be substantially degradable whendisposed of to the environment and exposed to air and/or water. As usedherein, “biodegradable” is meant to represent that a material degradesfrom the action of naturally occurring microorganisms such as bacteria,fungi, and algae. Using biodegradable materials permits the formation ofbiodisintegratable materials. As used herein, “biodisintegratable” ismeant to represent that a portion of the nonwoven material biodegrades,leaving an amount of material that is not able to be seen by the unaidedeye.

In the present invention, it is also desired that the aliphaticpolyester polymer be compostable. As a result, nonwoven materialincluding the aliphatic polyester polymer will be substantiallycompostable when disposed of to the environment and exposed to airand/or water. As used herein, “compostable” is meant to represent that amaterial is capable of undergoing biological decomposition in a compostsite such that the material is not visually distinguishable and breaksdown into carbon dioxide, water, inorganic compounds, and biomass, at arate consistent with known compostable materials.

The second component of the thermoplastic composition is polyolefinmicrofibers. Polyolefins are known to those skilled in the art. Anypolyolefin capable of being fabricated into an article, such as amicrofiber, is believed suitable for use in the present invention.Exemplary of polyolefins suitable for use in the present invention arethe homopolymers and copolymers comprising repeating units formed fromone or more aliphatic hydrocarbons, including ethylene, propylene,butene, pentene, hexene, heptene, octene, 1,3-butadiene, and2-methyl-1,3-butadiene. The polyolefins may be high or low density andmay be generally linear or branched chain polymers. Methods of formingpolyolefins are known to those skilled in the art.

Polyolefins, such as those described above, are generally hydrophobic innature. As used herein, the term “hydrophobic” refers to a materialhaving a contact angle of water in air of at least 90 degrees. Incontrast, as used herein, the term “hydrophilic” refers to a materialhaving a contact angle of water in air of less than 90 degrees. For thepurposes of this application, contact angle measurements may bedetermined as set forth in Robert J. Good and Robert J. Stromberg, Ed.,in “Surface and Colloid Science—Experimental Methods”, Vol. 11, (PlenumPress, 1979), pages 63-70.

It is generally desired that both the aliphatic polyester polymer andthe polyolefin be melt processable. It is therefore desired that thealiphatic polyester polymer and the polyolefin exhibit a melt flow ratethat is beneficially between about 1 gram per 10 minutes to about 200grams per 10 minutes, suitably between about 10 grams per 10 minutes toabout 100 grams per 10 minutes, and more suitably between about 20 gramsper 10 minutes to about 40 grams per 10 minutes. The melt flow rate of amaterial may be determined according to ASTM Test Method D1238-Eincorporated in its entirety herein by reference.

In the present invention, the polyolefin is used in the form of amicrofiber. As used herein, the term “microfiber” is meant to refer to afibrous material having a diameter that is less than about 50micrometers, beneficially less than about 25 micrometers morebeneficially less than about 10 micrometers, suitably less than about 5micrometers, and most suitably less than about 1 micrometer.

In one embodiment of the present invention, the polyolefin microfibercomprises a percentage of the cross sectional area of a multicomponentfiber prepared from the thermoplastic composition of the presentinvention that is effective for the multicomponent fiber to exhibitdesirable melt strength, fiber mechanical strength, and fiber spinningproperties. In general, if the polyolefin microfiber comprises apercentage of the cross sectional area of a multicomponent fiber that istoo high, this generally results in a nonwoven material that will not besubstantially biodisintegratable or that will be difficult to produce.Conversely, if the polyolefin microfiber comprises a percentage of thecross sectional area of a multicomponent fiber that is too low, thisgenerally results in a nonwoven material that will not exhibit effectivestructural properties or that may be difficult to process. Thus, thepolyolefin microfiber desirably comprises a percentage of the crosssectional area of a multicomponent fiber that is beneficially less thanabout 20 percent of the cross sectional area of the multicomponentfiber, more beneficially less than about 15 percent of the crosssectional area of the multicomponent fiber, and suitably less than about10 percent of the cross sectional area of the multicomponent fiber.

As used herein, the term “fiber” or “fibrous” is meant to refer to amaterial wherein the length to diameter ratio of such material isgreater than about 10. Conversely, a “nonfiber” or “nonfibrous” materialis meant to refer to a material wherein the length to diameter ratio ofsuch material is about 10 or less.

The polyolefin is generally desired to be in the form of a microfiber soas to allow the polyolefin to effectively function as a structuralsupport within the thermoplastic composition so as to prevent asubstantial thermal dimensional-shrinkage of the thermoplasticcomposition during processing while generally maintaining a desireddegree of substantial biodegradability of the thermoplastic composition.

It is generally desired that the polyolefin microfibers be present inthe thermoplastic composition in an amount effective to result in thethermoplastic composition exhibiting desired properties. The polyolefinmicrofibers will be present in the thermoplastic composition in a weightamount that is beneficially between greater than 0 weight percent toabout 45 weight percent, suitably between about 5 weight percent toabout 40 weight percent, and more suitably between about 10 weightpercent to about 30 weight percent, wherein all weight percents arebased on the total weight amount of the aliphatic polyester polymer, thepolyolefin microfiber, and the compatibilizer present in thethermoplastic composition. It is generally important for the polyolefinto be a substantially discontinuous phase of the thermoplasticcomposition so that the polyolefin microfibers can provide structuralsupport to the thermoplastic composition or materials formed from thethermoplastic composition, such as fibers or nonwovens, withoutnegatively affecting the biodegradability of the aliphatic polyester orof the substantial biodegradability of the thermoplastic composition ormaterials formed from the thermoplastic composition.

Either separately or when mixed together, the aliphatic polyesterpolymer and the polyolefin microfiber are generally hydrophobic.However, it is generally desired that the thermoplastic composition usedin the present invention, and nonwoven materials prepared from thethermoplastic composition, generally be hydrophilic so that suchmaterials are useful in disposable absorbent products which are insultedwith aqueous liquids such as water, urine, menses, or blood. Thus, ithas been found desirable to use another component as a surfactant in thethermoplastic composition of the present invention in order to achievethe desired hydrophilic properties.

Furthermore, it has been found desirable to improve the processabilityof the aliphatic polyester polymer and the polyolefin microfibers, sincesuch polymers are not chemically identical and are, therefore, somewhatincompatible with each other which tends to negatively affect theprocessing of a mixture of such polymers. For example, the aliphaticpolyester polymer and the polyolefin microfibers are sometimes difficultto effectively mix and prepare as an essentially homogeneous mixture ontheir own. Generally, then, it has been found desirable to use acompatibilizer to aid in the effective preparation and processing of thealiphatic polyester polymer and the polyolefin microfibers into a singlethermoplastic composition.

Therefore, the third component in the thermoplastic composition is acompatibilizer for the aliphatic polyester polymer and the polyolefinmicrofibers. Compatibilizers suitable for use in the present inventionwill generally comprise a hydrophilic section which will generally becompatible to the aliphatic polyester polymer and a hydrophobic sectionwhich will generally be compatible to the polyolefin microfibers. Thesehydrophilic and hydrophobic sections will generally exist in separateblocks so that the overall compatibilizer structure may be di-block orrandom block. It is generally desired that the compatibilizer initiallyfunctions as a plasticizer in order to improve the preparation andprocessing of the thermoplastic composition. It is then generallydesired that the compatibilizer serves as a surfactant in a materialprocessed from the thermoplastic composition, the nonwoven material ofthe present invention, by modifying the contact angle of water in air ofthe processed material. The hydrophobic portion of the compatibilizermay be, but is not limited to, a polyolefin such as polyethylene orpolypropylene. The hydrophilic portion of the compatibilizer may containethylene oxide, ethoxylates, glycols, alcohols or any combinationsthereof. Examples of suitable compatibilizers include UNITHOX®480 andUNITHOX®750 ethoxylated alcohols, or UNICID® Acid Amide Ethoxylates, allavailable from Petrolite Corporation of Tulsa, Okla.

It is generally desired that the compatibilizer exhibit a weight averagemolecular weight that is effective for the thermoplastic composition toexhibit desirable melt strength, fiber mechanical strength, and fiberspinning properties. In general, if the weight average molecular weightof a compatibilizer is too high, the compatibilizer will not blend wellwith the other components in the thermoplastic composition because thecompatibilizer's viscosity will be so high that it lacks the mobilityneeded to blend. Conversely, if the weight average molecular weight ofthe compatibilizer is too low, this represents that the compatibilizerwill generally not blend well with the other components and have such alow viscosity that it causes processing problems. Thus, compatibilizerssuitable for use in the present invention exhibit weight averagemolecular weights that are beneficially between about 1,000 to about100,000, suitably between about 1,000 to about 50,000, and more suitablybetween about 1,000 to about 10,000. The weight average molecular weightfor a compatibilizer material can be determined using methods known tothose skilled in the art.

It is generally desired that the compatibilizer exhibit an effectivehydrophilic-lipophilic balance ratio (HLB ratio). The HLB ratio of amaterial describes the relative ratio of the hydrophilicity of thematerial. The HLB ratio is calculated as the weight average molecularweight of the hydrophilic portion divided by the total weight averagemolecular weight of the material, which value is then multiplied by 20.If the HLB ratio value is too low, the material will generally notprovide the desired improvement in hydrophilicity. Conversely, if theHLB ratio value is too high, the material will generally not blend intothe thermoplastic composition because of chemical incompatibility anddifferences in viscosities with the other components. Thus,compatibilizers useful in the present invention exhibit HLB ratio valuesthat are beneficially between about 10 to about 40, suitably betweenabout 10 to about 20, and more suitably between about 12 to about 18.

It is generally desired that the compatibilizer be present in thethermoplastic composition in an amount effective to result in thethermoplastic composition exhibiting desired properties. In general, aminimal amount of the compatibilizer will be needed to achieve aneffective blending and processing with the other components in thethermoplastic composition. In general, too much of the compatibilizerwill lead to processing problems of the thermoplastic composition. Thecompatibilizer will be present in the thermoplastic composition in aweight amount that is beneficially between about 3 weight percent toabout 25 weight percent, more beneficially between about 10 weightpercent to about 25 weight percent, suitably between about 12 weightpercent to about 20 weight percent, and more suitably between about 13weight percent to about 18 weight percent, wherein all weight percentsare based on the total weight amount of the aliphatic polyester polymer,the polyolefin microfiber, and the compatibilizer present in thethermoplastic composition.

While the principal components of the thermoplastic composition havebeen described in the foregoing, such thermoplastic composition is notlimited thereto and can include other components not adversely effectingthe desired properties of the resulting biodisintegratable nonwovenmaterials. Exemplary materials which could be used as additionalcomponents would include, without limitation, pigments, antioxidants,stabilizers, surfactants, waxes, flow promoters, solid solvents,plasticizers, nucleating agents, particulates, and materials added toenhance processability of the thermoplastic composition. If suchadditional components are included in a thermoplastic composition, it isgenerally desired that such additional components be used in an amountthat is beneficially less than about 5 weight percent, more beneficiallyless than about 3 weight percent, and suitably less than about 1 weightpercent, wherein all weight percents are based on the total weightamount of the aliphatic polyester polymer, the polyolefin microfiber,and the compatibilizer present in the thermoplastic composition.

The thermoplastic composition used in the present invention is generallythe resulting morphology of a mixture of the aliphatic polyesterpolymer, the polyolefin polymer, the compatibilizer, and, optionally,any additional components. The polyolefin polymer forms a substantiallydiscontinuous phase encased within the aliphatic polyester polymersubstantially continuous phase. In order to achieve the desiredproperties for the thermoplastic composition, it is desirable that thealiphatic polyester polymer, the polyolefin microfibers, and thecompatibilizer remain substantially unreacted with each other. As such,each of the aliphatic polyester polymer, the polyolefin microfibers, andthe compatibilizer remain distinct components of the thermoplasticcomposition. Furthermore, it is desired that the aliphatic polyesterpolymer forms a substantially continuous phase and that the polyolefinmicrofibers form a substantially discontinuous phase, wherein thealiphatic polyester polymer continuous phase substantially encases thepolyolefin microfibers within its structure. As used herein, the term“encase”, and related terms, are intended to mean that the aliphaticpolyester polymer continuous phase substantially encloses or surroundsthe polyolefin microfibers.

In one embodiment of the present invention, after dry mixing togetherthe aliphatic polyester polymer, the polyolefin polymer, and thecompatibilizer to form a thermoplastic composition dry mixture, suchthermoplastic composition dry mixture is beneficially agitated, stirred,or otherwise blended to effectively uniformly mix the aliphaticpolyester polymer, the polyolefin polymer, and the compatibilizer suchthat an essentially homogeneous dry mixture is formed. The dry mixturemay then be melt blended in, for example, an extruder, to effectivelyuniformly mix the aliphatic polyester polymer, the polyolefin polymer,and the compatibilizer such that an essentially homogeneous meltedmixture is formed. The essentially homogeneous melted mixture may thenbe cooled and pelletized. Alternatively, the essentially homogeneousmelted mixture may be sent directly to a spin pack or other equipmentfor forming fibers or a nonwoven structure.

Alternative methods of mixing together the components include firstmixing together the aliphatic polyester polymer and the polyolefinpolymer and then adding the compatibilizer to such a mixture in, forexample, an extruder being used to mix the components together. Inaddition, it is also possible to initially melt mix all of thecomponents together at the same time. Other methods of mixing togetherthe components of the present invention are also possible and will beeasily recognized by one skilled in the art.

The present invention also utilizes a multicomponent fiber which isprepared from the thermoplastic composition previously described. Forpurposes of illustration only, the present description will generally bein terms of a multicomponent fiber comprising only three components.However, it should be understood that the biodisintegratable nonwovenmaterials of the present invention may include fibers with three or morecomponents. In one embodiment, the thermoplastic composition may be usedto form the sheath of a multicomponent fiber while a polyolefin, such aspolypropylene or polyethylene, is used to form the core. Suitablestructural geometries for multicomponent fibers include pie shape orside by side configurations.

With the aliphatic polyester polymer forming a substantially continuousphase, the aliphatic polyester polymer will generally provide an exposedsurface on at least a portion of the multicomponent fiber which willgenerally permit thermal bonding of the multicomponent fiber to otherfibers which may be the same or different from the multicomponent fiber.As a result, the multicomponent fiber can then be used to form thermallybonded fibrous nonwoven structures such as a nonwoven web. Thepolyolefin microfibers in the multicomponent fiber generally providestrength or rigidity to the multicomponent fiber and, thus, to anynonwoven structure comprising the multicomponent fiber. In order toprovide such strength or rigidity to the multicomponent fiber, it isgenerally desired that the polyolefin microfibers be substantiallycontinuous along the length of the multicomponent fiber.

Typical conditions for thermally processing the various componentsinclude using a shear rate that is beneficially between about 100seconds⁻¹ to about 10000 seconds⁻¹, more beneficially between about 500seconds⁻¹ to about 5000 seconds⁻¹, suitably between about 1000 seconds⁻¹to about 2000 seconds⁻¹, and most suitably at about 1000 seconds⁻¹.Typical conditions for thermally processing the components also includeusing a temperature that is beneficially between about 100° C. to about500° C., more beneficially between about 150° C. to about 300° C., andsuitably between about 175° C. to about 250° C.

Methods for making multicomponent fibers are well known and need not bedescribed here in detail. The melt spinning of polymers includes theproduction of continuous filament, such as spunbond or meltblown, andnon-continuous filament, such as staple and short-cut fibers,structures. To form a spunbond or meltblown fiber, generally, athermoplastic composition is extruded and fed to a distribution systemwhere the thermoplastic composition is introduced into a spinneretplate. The spun fiber is then cooled, solidified, and drawn by anaerodynamic system, to be formed into a conventional nonwoven.Meanwhile, to produce short-cut or staple fiber, rather than beingdirectly formed into a nonwoven structure, the spun fiber is cooled,solidified, and drawn, generally by a mechanical rolls system, to anintermediate filament diameter and collected. Subsequently, the fibermay be “cold drawn” at a temperature below its softening temperature, tothe desired finished fiber diameter and crimped or texturized and cutinto a desirable fiber length.

The process of cooling an extruded thermoplastic composition to ambienttemperature is usually achieved by blowing ambient or sub-ambienttemperature air over the extruded thermoplastic composition. It can bereferred to as quenching or super-cooling because the change intemperature is usually greater than 100° C. and most often greater than150° C. over a relatively short time frame, such as in seconds.

Multicomponent fibers can be cut into relatively short lengths such asstaple fibers which generally have lengths in the range of about 25 toabout 50 millimeters and short-cut fibers which are even shorter andgenerally have lengths less than about 18 millimeters. See, for example,U.S. Pat. No. 4,789,592 to Taniguchi et al, and U.S. Pat. No. 5,336,552to Strack et al., both of which are incorporated herein by reference intheir entirety.

The resultant multicomponent fibers are desired to exhibit animprovement in hydrophilicity, evidenced by a decrease in the contactangle of water in air. The contact angle of water in air of a fibersample can be measured as either an advancing or a receding contactangle value because of the nature of the testing procedure. Theadvancing contact angle generally measures a material's initial responseto a liquid, such as water. The receding contact angle generally gives ameasure of how a material will perform over the duration of a firstinsult, or exposure to liquid, as well as over following insults. Alower receding contact angle means that the material is becoming morehydrophilic during the liquid exposure and will generally then be ableto transport liquids more consistently. The receding contact angle datais used to establish the highly hydrophilic nature of a multicomponentfiber of the present invention although it is preferable that a decreasein the advancing contact angle of the multicomponent fiber also takesplace.

Thus, in one embodiment, it is desired that the thermoplasticcomposition or a multicomponent fiber exhibit a Receding Contact Anglevalue that is beneficially less than about 55 degrees, more beneficiallyless than about 40 degrees, suitably less than about 25 degrees, moresuitably less than about 20 degrees, and most suitably less than about10 degrees, wherein the receding contact angle is determined by themethod that is described in the Test Methods section herein.

Typical aliphatic polyester-based materials often undergo heat shrinkageduring downstream thermal processing. The heat-shrinkage mainly occursdue to the thermally-induced chain relaxation of the polymer segments inthe amorphous phase and incomplete crystalline phase. To overcome thisproblem, it is generally desirable to maximize the crystallization ofthe material before the bonding stage so that the thermal energy goesdirectly to melting rather than to allow for chain relaxation andreordering of the incomplete crystalline structure. The typical solutionto this problem is to subject the material to a heat-setting treatment.As such, when prepared materials, such as fibers, are subjected toheat-setting upon reaching a bonding roll, the fibers won'tsubstantially shrink because such fibers are already fully or highlyoriented. The present invention alleviates the need for this additionalprocessing step because of the morphology of the multicomponent fiber.As discussed earlier, the polyolefin microfibers generally provide areinforcing structure which minimizes the expected heat shrinkage of thealiphatic polyester.

In one embodiment, it is desired that the nonwoven material utilize athermoplastic composition or a multicomponent fiber which exhibits anamount of shrinking, as quantified by a Heat Shrinkage value, at atemperature of about 100° C., that is beneficially less than about 10percent, more beneficially less than about 5 percent, suitably less thanabout 2 percent, and more suitably less than about 1 percent, whereinthe amount of shrinking is based upon the difference between the initialand final lengths of a fiber divided by the initial length multiplied by100. The method by which the amount of shrinking that a fiber exhibitsmay be determined is included in the Test Methods section herein.

The resultant thermoplastic composition and multicomponent fibers areused to form biodisintegratable nonwoven materials which exhibit anincrease in high contact angle hysteresis values, quicker intake timesfor insults, and improved skin dryness, while also keeping very highwetting rates

The biodisintegratable nonwoven materials of the present invention aresuited for use in disposable products including disposable absorbentproducts such as diapers, adult incontinent products, and bed pads; incatamenial devices such as sanitary napkins, and tampons; and otherabsorbent products such as wipes, bibs, wound dressings, and surgicalcapes or drapes. Accordingly, in another aspect, the present inventionrelates to a disposable absorbent product comprising the nonwovenmaterial previously described.

In one embodiment of the present invention, the multicomponent fibersare formed into a fibrous matrix for incorporation into a disposableabsorbent product. A fibrous matrix may take the form of, for example, afibrous nonwoven web. Fibrous nonwoven webs may be made completely fromthe multicomponent fibers or they may be blended with other fibers. Thelength of the fibers used may depend on the particular end usecontemplated. Where the fibers are to be degraded in water as, forexample, in a toilet, it is advantageous if the lengths are maintainedat or below about 15 millimeters.

In one embodiment of the present invention, a disposable absorbentproduct is provided, which disposable absorbent product generallycomprises a composite structure including a liquid-permeable topsheet, afluid acquisition layer, an absorbent structure, and aliquid-impermeable backsheet, wherein at least one of theliquid-permeable topsheet, the fluid acquisition layer, or theliquid-impermeable backsheet comprises the nonwoven material of thepresent invention. In some instances, it may be beneficial for all threeof the topsheet, the fluid acquisition layer, and the backsheet tocomprise the nonwoven material of the present invention.

In another embodiment, the disposable absorbent product may comprisegenerally a composite structure including a liquid-permeable topsheet,an absorbent structure, and a liquid-impermeable backsheet, wherein atleast one of the liquid-permeable topsheet or the liquid-impermeablebacksheet comprises the nonwoven material of the present invention.

In another embodiment of the present invention, the nonwoven materialmay be prepared on a spunbond line. Resin pellets comprising thethermoplastic materials previously described are formed and predried.Then, they are fed to a single extruder. The fibers may be drawn througha fiber draw unit (FDU) or air-drawing unit onto a forming wire andthermally bonded. However, other methods and preparation techniques mayalso be used.

Exemplary disposable absorbent products are generally described in U.S.Pat. No. 4,710,187; U.S. Pat. No. 4,762,521; U.S. Pat. No. 4,770,656;and U.S. Pat. No. 4,798,603; which references are incorporated herein byreference.

Absorbent products and structures according to all aspects of thepresent invention are generally subjected, during use, to multipleinsults of a body liquid. Accordingly, the absorbent products andstructures are desirably capable of absorbing multiple insults of bodyliquids in quantities to which the absorbent products and structureswill be exposed during use. The insults are generally separated from oneanother by a period of time.

TEST METHODS

Melting Temperature

The melting temperature of a material was determined using differentialscanning calorimetry. A differential scanning calorimeter, under thedesignation Thermal Analyst 2910 Differential Scanning Calorimeter,which was outfitted with a liquid nitrogen cooling accessory and used incombination with Thermal Analyst 2200 analysis software (version 8.10)program, both available from T.A. Instruments Inc. of New Castle, Del.,was used for the determination of melting temperatures.

The material samples tested were either in the form of fibers or resinpellets. It was preferred to not handle the material samples directly,but rather to use tweezers and other tools, so as not to introduceanything that would produce erroneous results. The material samples werecut, in the case of fibers, or placed, in the case of resin pellets,into an aluminum pan and weighed to an accuracy of 0.01 mg on ananalytical balance. If needed, a lid was crimped over the materialsample onto the pan.

The differential scanning calorimeter was calibrated using an indiummetal standard and a baseline correction performed, as described in themanual for the differential scanning calorimeter. A material sample wasplaced into the test chamber of the differential scanning calorimeterfor testing and an empty pan is used as a reference. All testing was runwith a 55 cubic centimeter/minute nitrogen (industrial grade) purge onthe test chamber. The heating and cooling program was a 2 cycle testthat begins with equilibration of the chamber to −75° C., followed by aheating cycle of 20° C./minute to 220° C., followed by a cooling cycleat 20° C./minute to −75° C., and then another heating cycle of 20°C./minute to 220° C.

The results were evaluated using the analysis software program whereinthe glass transition temperature (Tg) of inflection, endothermic andexothermic peaks were identified and quantified. The glass transitiontemperature was identified as the area on the line where a distinctchange in slope occurs and then the melting temperature is determinedusing an automatic inflection calculation.

Apparent Viscosity

A capillary rheometer, under the designation Göttfert Rheograph 2003capillary rheometer, which was used in combination with WinRHEO (version2.31) analysis software, both available from Gottfert Company of RockHill, S.C., was used to evaluate the apparent viscosity rheologicalproperties of material samples. The capillary rheometer setup included a2000 bar pressure transducer and a 30 mm length/30 mm active length/1 mmdiameter/0 mm height/180° run in angle, round hole capillary die.

If the material sample being tested demonstrated or was known to havewater sensitivity, the material sample was dried in a vacuum oven aboveits glass transition temperature, i.e. above 55 or 60° C. forpoly(lactic acid) materials, under a vacuum of at least 15 inches ofmercury with a nitrogen gas purge of at least 30 standard cubic feet perhour for at least 16 hours.

Once the instrument was warmed up and the pressure transducer wascalibrated, the material sample was loaded incrementally into thecolumn, packing resin into the column with a ramrod each time to ensurea consistent melt during testing. After material sample loading, a 2minute melt time preceded each test to allow the material sample tocompletely melt at the test temperature. The capillary rheometer tookdata points automatically and determined the apparent viscosity (inPascal.second) at 7 apparent shear rates (in second⁻¹): 50, 100, 200,500, 1000, 2000, and 5000. When examining the resultant curve it wasimportant that the curve be relatively smooth. If there were significantdeviations from a general curve from one point to another possibly dueto air in the column, the test run was repeated to confirm the results.

The resultant rheology curve of apparent shear rate versus apparentviscosity gives an indication of how the material sample will run atthat temperature in an extrusion process. The apparent viscosity valuesat a shear rate of at least 1000 second⁻¹ are of specific interestbecause these are the typical conditions found in commercial fiberspinning extruders.

Molecular Weight

A gas permeation chromatography (GPC) method was used to determine themolecular weight distribution of samples, such as of poly(lactic acid)whose weight average molecular weight (M_(w)) is between about 800 toabout 400,000.

The GPC was set up with two PL gel Mixed K linear 5 micron, 7.5×300millimeter analytical columns in series. The column and detectortemperatures were 30° C. The mobile phase was high-performance liquidchromatography (HPLC) grade tetrahydrofuran (THF). The pump rate was 0.8milliliter per minute with an injection volume of 25 microliters. Totalrun time was 30 minutes. It is important to note that new analyticalcolumns must be installed about every 4 months, a new guard column aboutevery month, and a new in-line filter about every month.

Standards of polystyrene polymers, obtained from Aldrich Chemical Co.,were mixed into a solvent of dichloromethane(DCM):THF (10:90), both HPLCgrade, to obtain 1 mg/mL concentrations. Multiple polystyrene standardscould be combined in one standard solution provided that their peaks donot overlap when chromatographed. A range of standards of about 687 to400,000 molecular weight were prepared. Examples of standard mixtureswith Aldrich polystyrenes of varying weight average molecular weightsinclude: Standard 1 (401,340; 32,660; 2,727), Standard 2 (45,730;4,075), Standard 3 (95,800; 12,860) and Standard 4 (184,200; 24,150;687).

Next, the stock check standard was prepared. First, 10 g of a 200,000molecular weight poly(lactic acid) standard, Catalog#19245 obtained fromPolysciences Inc., was dissolved to 100 ml of HPLC grade DCM in a glassjar with a lined lid using an orbital shaker (at least 30 minutes).Next. the mixture was poured out onto a clean, dry, glass plate and thesolvent allowed to evaporate, then placed in a 35° C. preheated vacuumoven and dried for about 14 hours under a vacuum of 25 mm of mercury.Next, the poly(lactic acid) was removed from the oven and the film cutinto small strips. Immediately, the samples were ground using a grindingmill (with a 10 mesh screen) taking care not to add too much sample andcausing the grinder to freeze up. A few grams of the ground sample werestored in a dry glass jar in a dessicator, while the remainder of thesample can be stored in the freezer in a similar type jar.

It was important to prepare a new check standard prior to the beginningof each new sequence and, because the molecular weight is greatlyaffected by sample concentration, great care should be taken in itsweighing and preparation. To prepare the check standard, 0.0800 g±0.0025g of 200,000 weight average molecular weight poly(lactic acid) referencestandard was weighed out into a clean dry scintillation vial. Then,using a volumetric pipette or dedicated repipet, 2 ml of DCM was addedto the vial and the cap screwed on tightly. The sample was allowed todissolve completely. The sample was swirled on an orbital shaker, suchas a Thermolyne Roto Mix (type 51300) or similar mixer, if necessary. Toevaluate whether was it dissolved, the vial was held up to the light ata 45° angle. The vial was turned slowly and the liquid watched as itflowed down the glass. If the bottom of the vial did not appear smooth,the sample was not completely dissolved. It may take the sample severalhours to dissolve. Once dissolved, 18 ml of THF was added using avolumetric pipette or dedicated repipet, the vial capped tightly andmix.

Sample preparations began by weighing 0.0800 g±0.0025 g of the sampleinto a clean, dry scintillation vial (great care should also be taken inits weighing and preparation). 2 ml of DCM was added to the vial with avolumetric pipette or dedicated repipette and the cap screwed ontightly. The sample was allowed to dissolve completely using the sametechnique described in the check standard preparation above. Then 18 mlof THF was added using a volumetric pipette or dedicated repipette, thevial capped tightly and mixed.

The evaluation was begun by making a test injection of a standardpreparation to test the system equilibration. Once equilibration wasconfirmed the standard preparations were injected. After those were run,first the check standard preparation was injected and then the samplepreparations. The check standard preparation was injected after every 7sample injections and at the end of testing. Be careful not to take anymore than two injections from any one vial, and those two injectionsmust be made within 4.5 hours of each other.

There are 4 quality control parameters to assess the results. First, thecorrelation coefficient of the fourth order regression calculated foreach standard should be not less than 0.950 and not more than 1.050.Second, the relative standard deviation of all the weight averagemolecular weights of the check standard preparations should not be morethan 5.0 percent. Third, the average of the weight average molecularweights of the check standard preparation injections should be within 10percent of the weight average molecular weight on the first checkstandard preparation injection. Lastly, record the lactide response forthe 200 microgram per milliliter (μg/mL) standard injection on a SQCdata chart. Using the chart's control lines, the response must be withinthe defined SQC parameters.

Calculate the Molecular statistics based on the calibration curvegenerated from the polystyrene standard preparations and constants forpoly(lactic acid) and polystyrene in THF at 30° C. Those are:Polystyrene (K=14.1*10⁵, alpha=0.700) and poly(lactic acid) (K=54.9*10⁵,alpha=0.639).

Heat Shrinkage of Fibers

The required equipment for the determination of heat shrinkage include:a convection oven (Thelco model 160DM laboratory oven, available fromPrecision and Scientific Inc., of Chicago, Ill.), 0.5 g (+/−0.06 g)sinker weights, 1 inch binder clips, masking tape, graph paper with atleast 1 inch squares, foam posterboard (11 by 14 inches) or equivalentsubstrate to attach the graph paper and samples to. The convection ovenshould be capable of a temperature of about 100° C.

Fiber samples are melt spun at their respective spinning conditions. Ingeneral, a 30 filament bundle is preferred and mechanically drawn toobtain fibers with a jetstretch ratio of beneficially 224 or higher.Only fibers of the same jetstretch ratio can be compared to one anotherin regards to their heat shrinkage. The jetstretch ratio of a fiber isthe ratio of the speed of the drawdown roll divided by the linearextrusion rate (distance/time) of the melted polymer exiting thespinneret. The spun fiber is usually collected onto a bobbin using awinder. The collected fiber bundle was separated into 30 filaments, if a30 filament bundle has not already been obtained, and cut into 9 inchlengths.

The graph paper was taped onto the posterboard where one edge of thegraph paper was matched with the edge of the posterboard. One end of thefiber bundle was taped, no more than the end 1 inch. The taped end wasclipped to the posterboard at the edge where the graph paper was matchedup such that the edge of the clip rests over one of the horizontal lineson the graph paper while holding the fiber bundle in place (the tapedend should be barely visible as it is secured under the clip). The otherend of the bundle was pulled taught and lined up parallel to thevertical lines on the graph paper. Next, at 7 inches down from the pointwhere the clip is binding the fiber, the 0.5 g sinker was pinched aroundthe fiber bundle. The attachment process was repeated for eachreplicate. Usually, 3 replicates could be attached at one time. Markscould be made on the graph paper to indicate the initial positions ofthe sinkers. The samples were placed into the oven at a temperature ofabout 100° C. such that the samples hung vertically and did not touchthe posterboard. At time intervals of 5, 10 and 15 minutes quickly thenew location of the sinkers was marked on the graph paper and samplesreturned to the oven.

After the testing was complete, the posterboard was removed and thedistances between the origin (where the clip held the fibers) and themarks at 5, 10 and 15 minutes were measured with a ruler graduated to{fraction (1/16)} inch. Three replicates per sample is recommended.Calculate averages, standard deviations and percent shrinkage. Thepercent shrinkage is calculated as (initial length—measured length)divided by the initial length and multiplied by 100. As reported in theexamples herein and as used throughout the claims, the Heat Shrinkagevalue represents the amount of heat shrinkage that a fiber sampleexhibits at a temperature of about 100° C. for a time period of about 15minutes, as determined according to the preceding test method.

Contact Angle

The equipment includes a DCA-322 Dynamic Contact Angle Analyzer andWinDCA (version 1.02) software, both available from ATI-CAHNInstruments, Inc., of Madison, Wis. Testing was done on the “A” loopwith a balance stirrup attached. Calibrations should be done monthly onthe motor and daily on the balance (100 mg mass used) as indicated inthe manual.

Thermoplastic compositions were spun into fibers and the freefall sample(jetstretch of 0) was used for the determination of contact angle. Careshould be taken throughout fiber preparation to minimize fiber exposureto handling to ensure that contamination is kept to a minimum. The fibersample was attached to the wire hanger with scotch tape such that 2-3 cmof fiber extended beyond the end of the hanger. Then the fiber samplewas cut with a razor so that approximately 1.5 cm was extending beyondthe end of the hanger. An optical microscope was used to determine theaverage diameter (3 to 4 measurements) along the fiber.

The sample on the wire hanger was suspended from the balance stirrup onloop “A”. The immersion liquid was distilled water and it was changedfor each specimen. The specimen parameters were entered (i.e. fiberdiameter) and the test started. The stage advanced at 151.75microns/second until it detected the Zero Depth of Immersion when thefiber contacted the surface of the distilled water. From the Zero Depthof Immersion, the fiber advanced into the water for 1 cm, dwelled for 0seconds and then immediately receded 1 cm. The auto-analysis of thecontact angle done by the software determined the advancing and recedingcontact angles of the fiber sample based on standard calculationsidentified in the manual. Contact angles of 0 or <0 indicate that thesample had become totally wettable. Five replicates for each sample weretested and a statistical analysis for mean, standard deviation, andcoefficient of variation percent was calculated. As reported in theexamples herein and as used throughout the claims, the Advancing ContactAngle value represents the advancing contact angle of distilled water ona fiber sample determined according to the preceding test method.Similarly, as reported in the examples herein and as used throughout theclaims, the Receding Contact Angle value represents the receding contactangle of distilled water on a fiber sample determined according to thepreceding test method.

Fluid-Intake and Flowback Evaluation (FIFE)

Fluid-Intake and Flowback Evaluation (FIFE) testing was used todetermine the absorbency time and flowback of a personal care product. AMaster-Flex Digi-Staltic Automatic Dispensing system was supplied withsaline colored with a small amount of FD&C blue dye, set to provide 80mL insults, and dispensed several times to eliminate any air bubbles.The product samples, infant care diapers, were prepared without elasticsso that they would easily lie flat. Two 3.5 inch by 12 inch blotterpaper samples were weighed. These papers were placed on the FIFE board,a simple board with a 3 inch by 6 inch raised platform in the middle.The blotter papers were aligned so that they ran lengthwise along eitherside of the raised platform. The diaper was then aligned so that thearea to be insulted was carefully centered on the raised platform, withthe topsheet facing up, such that there were no visible wrinkles in thenonwoven topsheet. The second FIFE board was then placed on top of theproduct. This apparatus consists of a flat board that was intersected bya hollow cylinder, protruding only from the top side of the board. Thecircular region created where the cylinder intersected the flat plane ofthe board was hollow. The inner diameter of the cylinder was 5.1centimeters. A funnel with an inner diameter of 7 millimeters at theshort end was placed in the cylinder. The fluid was then dispensed bythe pump directly into the funnel. The intake time was recorded bystopwatch from the time the fluid hit the funnel to the moment no fluidwas visible on the specimen surface. The blotter papers were checked forproduct leakage and if any occurred the weight of the blotter paperswould have been measured to determine the quantity of fluid that leaked.In the described testing, no leakage occurred. Approximately one minuteelapsed before the second insult was applied in the same manner. Again athird insult was applied and timed in the same manner. If desired aprocedure may then follow to determine the amount of fluid flowing backwhen the product is under pressure. In this case, only the intake rateswere recorded.

TransEpidermal Water Loss (TEWL)

TransEpidermal Water Loss (TEWL) armband testing was used to measurechanges in skin hydration as a result of product use. A lowerevaporation value, as measured by a Servo Med Evaporimeter, isindicative of a product that promotes skindryness. This test actuallyreports a difference in evaporation values. A measurement of moistureevaporation rate is taken prior to the test and then immediatelyfollowing. The difference in these numbers provides the TEWL value asreported in the results. A lower TEWL value implies that a productprovides better breathability to the skin.

Product, in this case infant care diapers, was prepared by hand withoutany elastics or ears. The basic structure of the diaper was the same,but one control diaper consisted entirely of standard materials and theother had all standard materials except for the topsheet, which wascomprised of the biodisintegratable nonwoven. The target area for theinsults was drawn in permanent marker on the outside of the product. Alltesting occurred in a controlled environment of 72±4F with a relativehumidity of 40±5%. The subjects were adult women who were carefullyselected to insure that they had no conditions that might potentiallyalter the results of such a test.

Subjects relaxed in a controlled environment until a stable baselinereading of less than 10 g²/m/hr is obtained with the Servo MedEvaporimeter. These measurements were performed on the inner forearm ofthe subjects. Masterflex Digi-Staltic batch/dispense pump was used withsilicone tubing in the pump head, which was connected to neoprene tubingfor dispensing, by barb fittings. The end of the neoprene dispensingtube was placed oil the forearm of a subject and the product applied tothe forearm with the target insult area directly on top of the tubeopening. The product is secured with tape that was wrapped around thediaper and did not contact the skin. The diaper was then loaded withthree insults of 60 mL of saline at 45 second intervals and the tuberemoved. The product was further secured with a stretchable net and thesubject required to sit for one hour. After 60 minutes of wear, theproduct was removed and the Evaporimeter was then used to obtainreadings every second for two minutes in the same area on the forearm asthe baseline readings were taken. The reported result is the differencebetween the one-hour and baseline readings.

EXAMPLES Example 1

Fibers were prepared using varying amounts of a poly(lactic acid), apolypropylene, and a compatibilizer. The poly(lactic acid) polymer (PLA)was obtained from Chronopol Inc., Golden, Colorado, and had an L:D ratioof 100 to 0, a melting temperature of about 175° C., a weight averagemolecular weight of about 181,000, a number average molecular weight ofabout 115,000, a polydispersity index of about 1.57, and a residuallactic acid monomer value of about 2.3 weight percent. The polypropylenepolymer (PP) was obtained from Himont Incorporated under the designationPF305 polypropylene polymer, which had a specific gravity of betweenabout 0.88 to about 0.92 and a melting temperature of about 160° C. Thecompatibilizer was obtained from Baker-Petrolite Corporation of Tulsa,Okla., under the designation UNITHOX®480 ethoxylated alcohol, which hada melting temperature of about 160° C. and a number average molecularweight of about 2250.

To prepare a specific thermoplastic composition, the various componentswere first dry mixed and then melt blended in a counter-rotating twinscrew to provide vigorous mixing of the components. The melt mixinginvolves partial or complete melting of the components combined with theshearing effect of rotating mixing screws. Such conditions are conduciveto optimal blending and even dispersion of the components of thethermoplastic composition. Twin screw extruders such as a Haake Rheocord90, available from Haake GmbH of Karlsautte, Germany, or a Brabendertwin screw mixer (cat no 05-96-000) available from Brabender Instrumentsof South Hackensack, N.J., or other comparable twin screw extruders, arewell suited to this task. The melted composition is cooled followingextrusion from the melt mixer on either a liquid cooled roll or surfaceand/or by forced air passed over the extrudate. The cooled compositionis then subsequently pelletized for conversion to fibers.

Converting these resins into fiber and nonwoven was conducted on ain-house 0.75 inch diameter extruder with a 24:1 L:D (length:diameter)ratio screw and three heating zones which feed into a transfer pipe fromthe extruder to the spin pack, which constitutes the 4th heating zoneand contains a 0.62 inch (about 1.6 cm) diameter Koch® SMX type staticmixer unit, available from Koch Engineering Company Inc. of New York,N.Y., and then into the spinning head (5th heating zone) and through aspin plate which is simply a plate with numerous small holes throughwhich the molten polymer will be extruded through. The spin plate usedherein had 15 to 30 holes, where each hole has a diameter of about 500micrometers. The temperature of each heating zone is indicatedsequentially under the extrusion temperatures heading in Table 2. Thefibers are air quenched using air at a temperature range of 13° C. to22° C., and drawn down by a mechanical draw roll and passed on to eithera winder unit for collection, or to a fiber drawing unit for spunbondformation and bonding, or through accessory equipment for heat settingor other treatment before collection.

The fibers were evaluated for contact angle and hysteresis. Theadvancing angle is a measure of how a material will interact with fluidduring it's first contact with liquid. The receding angle is anindication of how the material will behave during multiple insults withliquid or in a damp, high humidity environment. Hysteresis is defined asthe difference between the advancing and receding contact angles of amaterial. A low hysteresis, in general, will provide a fast rate ofwetting. The composition of the various fibers and the results of theevaluations are shown in Table 1.

TABLE 1 Contact Angle Results Composition of Fiber Advancing Receding(wt %) Contact Contact (polylactide:polypropylene:Unithox) Angle AngleHysteresis 100:0:0* 85.3° 40.7° 44.6 0:100:0* 128.1° 93.9° 34.2 0:95:5* 120.6°   79° 41.6 0:95:5*  124.0° 58.5° 65.5 95:0:5*  89.2° 10.0° 79.270:30:0* 92.3° 56.5° 35.8 55:37:8  111.7° 51.4° 60.3 64:27:9  117.4°40.1° 77.3 48:39:13 106.3°   0° 106.3 52:35:13 97.6° 16.8° 80.8 61:26:1388.6°  5.8° 82.8 70:17:13 86.7°   0° 86.7 51:34:15 92.8°  3.3° 89.576.5:8.5:15  86.1°   0° 86.1 *Not an example of the present invention.

Note that the blends listed here have very high hysteresis values, inthe range of 60-110 degrees. In general, it is expected that a highhysteresis value will inhibit the rate of wetting. However, theunexpected result obtained was that these high hysteresis fibersdemonstrated very high rates of wetting as demonstrated by the nonwoventesting results.

Example 2

A nonwoven material sample of the present invention was prepared. Thesample comprised 61 wt % polylactide, 26 wt % polypropylene and 13 wt %UNITHOX® 480. This sample was compared to a current diaper liner controlin testing for fluid intake time for multiple insults, for skin drynessand for biodegradation of the material.

Fluid Intake Flowback Evaluation (FIFE) is used to determine the Intaketime of consecutive insults into an infant care product. Trans EpidermalWater Loss (TEWL) employs an evaporimeter to determine the rate of fluidevaporation from this skin. A lower evaporation rate implies drier skin.This test calculates a difference between a baseline evaporation rate,and the evaporation rate after wearing a product insulted with saline onthe forearm.

Biodegradability testing was performed by Organic Waste Systems Inc.according to ASTM 5338.92 modified so that testing was conductedisothermally at 58° C.

The nonwovens demonstrated improved fluid handling properties over thecurrent surfactant treated polypropylene as evidenced by the followingresults in Table 2.

TABLE 2 Nonwoven Testing Results Current Diaper Liner PLA/PP/UnithoxTest Control (61:26:13) FIFE- 1^(st) insult (sec.) 28.03 24.43 FIFE-2^(nd) insult (sec.) 83.30 60.05 FIFE- 3^(rd) insult (sec.) 94.98 65.88Skin Dryness - TEWL 21.57 17.16 (g/m²) % Biodegradation @ 0% 50.3% Day45

While a polypropylene sample was not run for the biodegradabilityexperiment, it is well known that polypropylene does not undergo anysignificant degradation. The polylactide in thepolylactide/polypropylene/Unithox (PPU) blend, however will degrade, andthe samples demonstrated 50.3% biodegradation after only 45 days. It islikely that after an extended period of time all of the PLA willdegrade.

The smaller intake time demonstrated by the PPU is essential forachieving dryness in a personal care product. This low intake time,indicates that the fluid insults are more rapidly drawn into theproduct. It is important to note that while intake time increases withconsecutive insults, it remains significantly better than thepolypropylene control, and the intake time is actually increasing at aslower rate than for the control. The control is a surfactant treatedpolypropylene, where the surfactant has a tendency to wash off duringconsecutive insults. The PPU has the further advantage that it isinherently wettable, and this wettability is more permanent. These fastintake times are somewhat of a surprise in light of the fact that thematerials have such high hysteresis values. This is a unique andunexpected result to achieve such quick intake rates at high hysteresisvalues.

The TEWL results give an indication of how dry the product, in this casean infant core diaper, will keep the skin of the baby wearing it. Forthis particular test a lower TEWL value is desired. This test employed acurrent diaper control and a diaper that was constructed with a PPUliner. As the results indicate, the PPU liner gave an average TEWLreading that was 20% lower than the current diaper liner. This is asignificant improvement in fluid management over the current polyolefinsystem.

In summary, the PPU nonwoven material has a greater degree ofbiodegradability than the existing polyolefin systems. This improvedbiodegradability can address some of the environmental concernsassociated with current personal care products. This biodegradabilitydoes not come at the sacrifice of performance, as demonstrated by theimproved fluid management properties. With a 28% reduction in TEWLvalue, and much faster intake rates, the PPU system will promote dryskin when implemented in a personal care product.

Those skilled in the art will recognize that the present invention iscapable of many modifications and variations without departing from thescope thereof. Accordingly, the detailed description and examples setforth above are meant to be illustrative only and are not intended tolimit, in any manner, the scope of the invention as set forth in theappended claims.

What is claimed is:
 1. A disposable absorbent product comprising aliquid-permeable topsheet, a fluid acquisition layer, an absorbentstructure, and a liquid-impermeable backsheet, wherein at least one ofthe liquid-permeable topsheet, the fluid acquisition layer, or theliquid-impermeable backsheet comprises a biodisintegratable nonwovenmaterial comprising a plurality of multicomponent fibers prepared from athermoplastic composition, wherein the thermoplastic compositioncomprises: a. an aliphatic polyester polymer in a weight amount that isbetween about 45 to about 90 weight percent, wherein the aliphaticpolyester polymer forms a substantially continuous phase; b. polyolefinmicrofibers in a weight amount that is between greater than 0 to about45 weight percent, wherein the polyolefin microfibers have a diameterthat is less than about 50 micrometers and the polyolefin microfibersform a substantially discontinuous phase encased within the aliphaticpolyester polymer substantially continuous phase; and c. acompatibilizer, which exhibits a hydrophilic-lipophilic balance ratiothat is between about 10 to about 40, in a weight amount that is betweenabout 7 to about 25 weight percent, wherein all weight percents arebased on the total weight amount of the aliphatic polyester polymer; thepolyolefin microfibers, and the compatibilizer present in thethermoplastic composition, wherein the multicomponent fiber exhibits aReceding Contact Angle value that is less than about 55 degrees.
 2. Thedisposable absorbent product of claim 1, wherein the multicomponentfiber exhibits a Heat Shrinkage value that is less than about 10percent.
 3. The disposable absorbent product of claim 1, wherein thealiphatic polyester polymer is selected from the group consisting ofpoly(lactic acid), polybutylene succinate, polybutylenesuccinate-co-adipate, polyhydroxybutyrate-co-valerate, polycaprolactone,sulfonated polyethylene terephthalate, mixtures of such polymers, andcopolymers of such polymers.
 4. The disposable absorbent product ofclaim 3, wherein the aliphatic polyester polymer is poly(lactic acid).5. The disposable absorbent product of claim 1, wherein the polyolefinis selected from the group consisting of homopolymers and copolymerscomprising repeating units selected from the group consisting ofethylene, propylene, butene, pentene, hexene, heptene, octene,1,3-butadiene, and 2-methyl-1,3-butadiene.
 6. The disposable absorbentproduct of claim 5, wherein the polyolefin is selected from the groupconsisting of polyethylene and polypropylene.
 7. The disposableabsorbent product of claim 1, wherein the polyolefin microfibers have adiameter that is less than about 25 micrometers.
 8. The disposableabsorbent product of claim 1, wherein the polyolefin microfibers arepresent in a weight amount that is between about 5 to about 40 weightpercent.
 9. The disposable absorbent product of claim 1, wherein thecompatibilizer is an ethoxylated alcohol.
 10. The disposable absorbentproduct of claim 1, wherein the aliphatic polyester polymer is selectedfrom the group consisting of poly(lactic acid), polybutylene succinate,polybutylene succinate-co-adipate, polyhydroxybutyrate-co-valerate,polycaprolactone, sulfonated polyethylene terephthalate, mixtures ofsuch polymers, and copolymers of such polymers; wherein the polyolefinis selected from the group consisting of homopolymers and copolymerscomprising repeating units selected from the group consisting ofethylene, propylene, butene, pentene, hexene, heptene, octene,1,3-butadiene, and 2-methyl-1,3-butadiene and the polyolefin microfibersare present in a weight amount that is between about 5 to about 40weight percent; the compatibilizer is an ethoxylated alcohol; and themulticomponent fiber exhibits a Heat Shrinkage value that is less thanabout 10 percent.
 11. The disposable absorbent product of claim 10,wherein the aliphatic polyester polymer is poly(lactic acid) and thepolyolefin is selected from the group consisting of polyethylene andpolypropylene.
 12. The disposable absorbent product of claim 1, whereinthe liquid-permeable topsheet, the fluid acquisition layer, and theliquid-impermeable backsheet comprise the biodisintegratable nonwovenmaterial comprising a plurality of multicomponent fibers prepared fromthe thermoplastic composition.
 13. A disposable absorbent productcomprising a liquid-permeable topsheet, an absorbent structure, and aliquid-impermeable backsheet, wherein at least one of theliquid-permeable topsheet or the liquid-impermeable backsheet comprisesa biodisintegratable nonwoven material comprising a plurality ofmulticomponent fibers prepared from a thermoplastic composition, whereinthe thermoplastic composition comprises: a. an aliphatic polyesterpolymer in a weight amount that is between about 45 to about 90 weightpercent, wherein the aliphatic polyester polymer forms a substantiallycontinuous phase; b. polyolefin microfibers in a weight amount that isbetween greater than 0 to about 45 weight percent, wherein thepolyolefin microfibers have a diameter that is less than about 50micrometers and the polyolefin microfibers form a substantiallydiscontinuous phase encased within the aliphatic polyester polymersubstantially continuous phase; and c. a compatibilizer, which exhibitsa hydrophilic-lipophilic balance ratio that is between about 10 to about40, in a weight amount that is between about 7 to about 25 weightpercent, wherein all weight percents are based on the total weightamount of the aliphatic polyester polymer; the polyolefin microfibers,and the compatibilizer present in the thermoplastic composition, whereinthe multicomponent fiber exhibits a Receding Contact Angle value that isless than about 55 degrees.
 14. The disposable absorbent product ofclaim 13, wherein the multicomponent fiber exhibits a Heat Shrinkagevalue that is less than about 10 percent.
 15. The disposable absorbentproduct of claim 13, wherein the aliphatic polyester polymer is selectedfrom the group consisting of poly(lactic acid), polybutylene succinate,polybutylene succinate-co-adipate, polyhydroxybutyrate-co-valerate,polycaprolactone, sulfonated polyethylene terephthalate, mixtures ofsuch polymers, and copolymers of such polymers.
 16. The disposableabsorbent product of claim 15, wherein the aliphatic polyester polymeris poly(lactic acid).
 17. The disposable absorbent product of claim 13,wherein the polyolefin is selected from the group consisting ofhomopolymers and copolymers comprising repeating units selected from thegroup consisting of ethylene, propylene, butene, pentene, hexene,heptene, octene, 1,3-butadiene, and 2-methyl-1,3-butadiene.
 18. Thedisposable absorbent product of claim 17, wherein the polyolefin isselected from the group consisting of polyethylene and polypropylene.19. The disposable absorbent product of claim 13, wherein the polyolefinmicrofibers have a diameter that is less than about 25 micrometers. 20.The disposable absorbent product of claim 13, wherein the polyolefinmicrofibers are present in a weight amount that is between about 5 toabout 40 weight percent.
 21. The disposable absorbent product of claim13, wherein the compatibilizer is an ethoxylated alcohol.
 22. Thedisposable absorbent product of claim 13, wherein the aliphaticpolyester polymer is selected from the group consisting of poly(lacticacid), polybutylene succinate, polybutylene succinate-co-adipate,polyhydroxybutyrate-co-valerate, polycaprolactone, sulfonatedpolyethylene terephthalate, mixtures of such polymers, and copolymers ofsuch polymers; wherein the polyolefin is selected from the groupconsisting of homopolymers and copolymers comprising repeating unitsselected from the group consisting of ethylene, propylene, butene,pentene, hexene, heptene, octene, 1,3-butadiene, and2-methyl-1,3-butadiene and the polyolefin microfibers are present in aweight amount that is between about 5 to about 40 weight percent; thecompatibilizer is an ethoxylated alcohol; and the multicomponent fiberexhibits a Heat Shrinkage value that is less than about 10 percent. 23.The disposable absorbent product of claim 22, wherein the aliphaticpolyester polymer is poly(lactic acid) and the polyolefin is selectedfrom the group consisting of polyethylene and polypropylene.
 24. Thedisposable absorbent product of claim 13, wherein the liquid-permeabletopsheet and the liquid-impermeable backsheet comprise thebiodisintegratable nonwoven material comprising a plurality ofmulticomponent fibers prepared from the thermoplastic composition.